Difference between Perspective, Isometric, Oblique and Orthographic Drawing.

Perspective drawing is a kind of pictorial drawing as they shows objects as they look to the eye.These are the two main features:
Smaller as their distance from the observer increases
Foreshortened: the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight
There are a few types of perspective drawing like linear perspective,aerial perspective and more.
http://en.wikipedia.org/wiki/Perspective_drawing
www.turbophoto.com/Perspective-Drawing-Definition/
http://www.stormthecastle.com/fantasyartschool/artlessons/lesson3.htm

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What is Isometric drawing ?It is a method of non perspective pictorial drawing in which the object being drawn is turned so that three mutually perpendicular edges are equally foreshortened.It is a method of visually representing three-dimensional objects in two dimensions, in which the three coordinate axes appear equally foreshortened and the angles between any two of them are 120 degrees.
http://www.answers.com/topic/isometric-drawing
Source:/en.wikipedia.org/wiki/Isometric_projection

source : http://www.we-r-here.com/cad_05/tutorials/level_3/images/isometric_dwg.gif

Oblique drawings are designed to show a three dimensional view of an object. The width of the object will still be drawn as a horizontal line, but the depth can be drawn back at any angle. You can choose the best angle to make the drawing look the best. There are three types of obliques, cavalier, normal, and cabinet obliques. Cabinet drawings are when the you cut the depth in half. Cavalier drawings are when you keep the depth the full measurement. Normal drawings are when you cut the depth by 3/4.
Source:/library.thinkquest.org/TQ0310106/oblique.html

source :https://rdl.train.army.mil/soldierPortal/atia/adlsc/view/public/9726-1/accp/en0113/en011360012.gifa

orthographic drawing is a drawing that communicates the shape and size of an object through a series of related two-dimensional views.
Source:http://wiki.answers.com/Q/Define_orthographic_drawing

source :http://www.helenhudspith.com/resources/graphics/room3.jpg